1. Field of the Invention
The present invention relates to a multi X-ray generating apparatus used for nondestructive radiography, diagnosis, and the like in the fields of medical equipment and industrial equipment which use X-ray sources, and an X-ray imaging apparatus using the multi X-ray generating apparatus.
2. Description of the Related Art
In general, an X-ray tube uses a thermion source as an electron source, transmits the thermions from a filament heated to a high temperature to a Wehnelt electrode, extraction electrode, acceleration electrode, and lens electrode, and accelerates an electron beam into a high-energy electron beam. After shaping the electron beam into a desired shape, the X-ray tube generates X-rays by irradiating an X-ray target made of a metal with the beam.
Recently, a cold cathode electron source has been developed as an electron source replacing this thermion source, and has been widely studied as the application of a combination with a flat panel detector (FPD). As a typical cold cathode, a Spindt type electron source is known, which extracts electrons by applying a high electric field to the tip of a needle with a size of several 10 nm. There are also available, for example, an electron emitter using a carbon nanotube (CNT) as a material and a surface conduction type electron source which emits electrons by forming a nanometer (nm)-order microstructure on the surface of a glass substrate.
Japanese Patent Laid-Open Nos. 09-180894 and 2004-329784 propose, as an application of these electron sources, a technique of extracting X-rays by forming a single electron beam using a Spindt type electron source or a carbon nanotube type electron source. Japanese Patent Laid-Open No. 08-264139 and Applied Physics Letters 86, 184104 (2005), J. Zhang “Stationary scanning x-ray source based on carbon nanotube field emitters” disclose a technique of generating X-rays by irradiating an X-ray target with electron beams from a multi electron source using a plurality of these cold cathode electron sources.
In addition, Japanese Patent Laid-Open No. 2007-265981 discloses an X-ray apparatus which forms X-ray beams from a multi X-ray source into multi X-ray beams with excellent characteristics without any mutual interference.
A rotating target type X-ray source is available as a conventional single-focus X-ray source. A method of generating X-rays with different radiation qualities by using this X-ray source has been proposed. As a concrete example of this method, Japanese Patent Laid-Open Nos. 05-028939 and 05-036368 disclose a method of respectively irradiating two types of target materials 102 and 102a placed on one rotating target 101 with electron beams, as shown in FIG. 13. In addition, Japanese Patent Laid-Open No. 01-204649 discloses a method of generating X-rays with different radiation qualities by arranging different target materials on the two surfaces of one rotating target and its applied method.
In a representative rotating target type X-ray source as a single-focus X-ray source, the number of types of radiation qualities which can be obtained from one tube is limited to about two because of restrictions in terms of the shapes of the electron source, target structure, and the like. In addition, since the number of focal spots of the X-ray source is also limited to about two, it is difficult to adjust radiation quality and dose conditions in accordance with a body part of an object and its shape and to obtain an X-ray image with high quality.